THz signal propagation models should also account for some widely ignored characteristics at lower frequency bands. For instance, spherical wave propagation (SWP) models should replace plane wave approximations that are inaccurate at THz frequencies and may lead to channel estimation errors in massive MIMO systems. In particular, hybrid spherical- and planar-wave channel modeling solutions are found to be sufficiently accurate and less complex than fully spherical wave models [1]}. Similarly, the beam squint effect, caused by frequency-independent steering vectors in wide-band massive MIMO THz beamforming, should be accounted for [2]}; ignoring such frequency dependency results in signals being steered into unintended physical directions.
